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Wireless Energy Harvesting by Direct Voltage Multiplication on Lateral Waves from a Suspended Dielectric Layer

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Wireless Energy Harvesting by Direct Voltage Multiplication on Lateral Waves from a Suspended Dielectric Layer SPECIAL SECTION ON ENERGY EFFICIENT WIRELESS COMMUNICATIONS WITH ENERGY HARVESTING AND WIRELESS POWER TRANSFER Received September 2, 2017, accepted September 26, 2017, date of publication September 29, 2017, date of current version November 7, 2017. Digital Object Identifier 10.1109/ACCESS.2017.2757947 Wireless Energy Harvesting by Direct Voltage Multiplication on Lateral Waves From a Suspended Dielectric Layer LOUIS WY LIU 1, QINGFENG ZHANG 1, YIFAN CHEN2, MOHAMMED A. TEETI1, AND RANJAN DAS1,3 1Electrical and Electronics Engineering Department, Southern University of Science and Technology, Shenzhen 154108, China 2School of Engineering, University of Waikato, Hamilton 3240, New Zealand 3School of Engineering, IIT Bombay, Mumbai 400076, India Corresponding author: Qingfeng Zhang ([email protected]) This work was supported in part by the Guangdong Natural Science Funds for Distinguished Young Scholar under Grant 2015A030306032, in part by the Guangdong Special Support Program under Grant 2016TQ03X839, in part by the National Natural Science Foundation of China under Grant 61401191, in part by the Shenzhen Science and Technology Innovation Committee funds under Grant KQJSCX20160226193445, Grant JCYJ20150331101823678, Grant KQCX2015033110182368, Grant JCYJ20160301113918121, Grant JSGG20160427105120572, and in part by the Shenzhen Development and Reform Commission Funds under Grant [2015] 944. ABSTRACT This paper explores the feasibility of wireless energy harvesting by direct voltage multiplication on lateral waves. Whilst free space is undoubtedly a known medium for wireless energy harvesting, space waves are too attenuated to support realistic transmission of wireless energy. A layer of thin stratified dielectric material suspended in mid-air can form a substantially less attenuated pathway, which efficiently supports propagation of wireless energy in the form of lateral waves. The conductivity of the suspended dielectric layer does not appear to be a critical factor rendering propagation of lateral waves impossible. In this paper, a mathematical model has been developed to simulate wireless energy harvesting over a suspended layer of stratified dielectric material. The model has been experimentally verified with the help of a novel open-ended voltage multiplier designed to harvest energy from ambient electromagnetic fields. INDEX TERMS Energy harvesting, stratified ground, Goubau line, Avremenko diode configurations, trapped surface waves, transverse magnetic modes, TM modes, TEM modes, Zenneck Waves, lateral waves, ground waves. I. INTRODUCTION Throughout the last century, there have been many unsuc- Whilst many researchers of this date are still struggling to cessful attempts to use Zenneck's version of surface waves to transmit wireless energy over just a few meters by mag- explain Marconi's work [8]–[12]. The absence of an appro- netic coupling, the feasibility of long range wireless energy priate theory for surface waves or their derivatives does not harvesting has long been proven beyond any doubt by necessarily mean that Marconi's achievement in long range Marconi [1]–[3]. In one of Marconi's early experiments, wireless power transfer (WPT) has to be erased from history. wireless energy was successfully and safely transmitted Towards the end of the last century, Wait came forwards with and harvested over 2 miles of a hilly area by grounding a concept of trapped surface waves in a stratified ground [13]. and lengthening monopole antenna as a way to reduce Trapped surface wave is an evanescent wave propagating by the aperture size of the antenna. Marconi concluded from successive internal reflections due to an incident electromag- his first breakthrough experiment that his antenna radi- netic wave striking at an interface with an angle greater than ated vertically polarized radio waves that could travel the critical angle. However, the energy from trapped surface distances much longer than other conventional counter- waves has not been found to be significant in many situa- parts. Later, he even achieved non-line-of-sight (NLOS) tions [14]. In the same decade, another much more promising propagation of wireless power across the Atlantic concept known as lateral wave was used by King to explain Ocean [4]–[7]. the dominant electromagnetic waves propagating over the 2169-3536 2017 IEEE. Translations and content mining are permitted for academic research only. VOLUME 5, 2017 Personal use is also permitted, but republication/redistribution requires IEEE permission. 21873 See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. L. W. Liu et al.: Wireless Energy Harvesting by Direct Voltage Multiplication on Lateral Waves surface of a stratified ground [15]. This lateral wave is a TABLE 1. Differences between space waves and surface waves. vertically polarized electromagnetic wave on the top surface of the ground as a result of an incident electromagnetic wave striking the air-ground interface from below at exactly the critical angle [16], [17]. For an interface between two different dielectric media, the critical angle is only applica- ble to the dielectric medium with a higher refractive index. To excite this lateral wave, it is logical to bury the lower end of transmitting and receiving aerials into the dielectric layer with a higher refractive index in much the same way as grounding a monopole antenna in Tesla's or Marconi's work [2], [16]–[18]. In fact, the vertically polarized radio wave as referred by Marconi or ground current referred by Nikola Tesla is most likely equivalent to the lateral wave referred by King, Tamir and many other researchers in the field of wireless energy harvesting. Ironically, most of the recently published systems for WPT are still based on space waves, including the magnetic cou- pled waves for near field applications and the Hertzian radio waves for far field applications. Space waves are known to be inefficient because a significant amount of energy in an unguided space wave is lost by radiation. On the other hand, transmitting a large electric power through free space will directly impose interference to the present communica- tion systems. Another little-known fact is that an extremely low-frequency space waves can potentially trigger release of toxins from microvesicles of monocytic leukaemia cells [19]. The authors believe that delivering electric power through the physical ground, ocean or the wall of a building is a far more logical solution. In this article, the feasibility of wireless energy harvesting by voltage multiplication on lateral waves is explored by an unconventional means. Instead of transmitting a wireless energy through a thick layer of a concrete ground, we extend the original idea of Tesla's or Marconi's to harvest a wireless energy from a thin layer of dielectric material suspended in mid-air. We begin our presentation by formulating a math- ematical model of electromagnetic waves associated with a dielectric layer suspended in mid-air. The theoretical work will be substantiated with the results of WPT experiments based on a little known open-ended voltage multiplier. Applications of lateral-wave-based WPT will be explored in areas of wireless communication according to the well understood differences between surface waves and space waves as summarized in Table 1. waves and lateral waves. The existence of trapped surface waves is possible if and only if the suspended layer of dielec- II. ELECTROMAGNETIC MODELING OF A SUSPENDED tric material is sufficiently thick, perhaps, thicker than half of LAYER OF A DIELECTRIC MATERIAL the wavelength. To rule out the possibility of trapped surface While stratified ground with a perfect conducting bot- waves being present to a significant extent, we have chosen to tom plane as a medium for transmission of trapped study the suspended dielectric layer with a thickness substan- surface waves and lateral waves has been extensively tially smaller than half of the wavelength. Examples of this studied [13]–[15], [20], the results of our investigation reveal stratified ground with imperfectly conducting bottom plane that a suspended layer of dielectric material can be modeled include a table top, an iron-reinforced concrete wall or any as a 4-layered stratified ground with imperfectly conduct- suspended dielectric layer coated with an oxide. ing ground. The stratified ground with imperfectly conduct- Fig. 1 illustrates how a suspended dielectric layer can be ing ground can support propagation of both trapped surface visualized as a conventional four-layered stratified ground 21874 VOLUME 5, 2017 L. W. Liu et al.: Wireless Energy Harvesting by Direct Voltage Multiplication on Lateral Waves layer j defined as q D 2 − 2 γj kj λ ; (3) Q, which is the reflection coefficient of the half-space due to the multi-layered configuration, can be expressed as: 2 k0 γ0 − Zs D − !µ0 Q 2 ; (4) k0 γ C Zs 0 !µ0 In (4), Zs represents the surface impedance for the 4-layered stratified ground configuration as defined in [15]: FIGURE 1. Configuration of wireless power transfer involving a dipole vertically mounted on the surface of a suspended dielectric layer. 2 2 2 2 − 2 3 γ1µ0!k1 γ2 k3 tan .γ2l2/ i γ2γ3k2 4 4 γ1γ3k2 tan .γ1l1/ tan .γ2l2/ 5 Cγ1µ0! 2 2 Ciγ1γ2k k tan .γ1l1/ with imperfect conducting plane at the bottom. This dielectric Z D 2 3 : (5) s 2 4 − 2 2 3 configuration is similar to the 4-layered ground that has iγ1γ3k2 tan .γ2l2/ γ1γ2k2 k3 2 C 2 2 3 already been considered in other studies [14], [20], with k1 4 γ2 k1 k3 tan .γ1l1/ tan .γ2l2/ 5 C 2 2 an exception that the bottom layer in the present work is iγ2γ3k1 k2 tan .γ1l1/ a layer of air with an extremely small conductivity. The The first and second integral terms on the right side of (2) relative permittivities of layers 0, 1, 2 and 3 are respectively represents the direct space wave and the reflected space wave "0, "1, "2 and "3, where "0 D "3D1. The thicknesses of respectively. These two integral terms have been evaluated by layer 0 and layer 3 is assumed to be infinity.
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